CoCoA » CoCoALib

The BOOST equivalent of bool3 is called tribool. It offers automatic conversion to and from bool.

I have already established that auto conversion from bool gives us problems (because the C++ compiler thinks that tribool is as good a match as MachineInt for any integral value). This was evident with operator<< for OpenMath streams.

While writing the matrix solve fn I wanted to test quickly whether a ring is a PID, because if so then there is a quick and simple algm to compute the answer. But testing whether a ring is a PID is costly; however, one can do a fast check which returns a bool3 result -- essentially it recognises some easy cases, otherwise it says it doesn't know. Compare the two lines of code below:

Currently we must convert explicitly from bool3 to bool like this:

    if (IsDefinitelyTrue(IsPIDFast(R))) return SolveByHNF(M, rhs);

If the conversion were automatic, the code could be simplified to this:

    if (IsPIDFast(R)) return SolveByHNF(M, rhs);

The difference is not huge. There is a trade-off between "safety" and readability.

In this case if the auto conversion maps DefinitelyTrue to true and the other values to false then we get simpler more readable code.

On the other hand if there is auto conversion then a careless user might write code blissfully unaware that IsPIDFast returns a bool3 -- I'm not sure if this can lead to serious problems.

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